Pillared Metal-organic Frameworks Research Articles

Construction of a Fluorinated-Anion Pillared Metal-Organic Framework Exhibiting Dual-Pore Architecture for Simultaneous Enhancement of C2H2 Adsorption Capacity and Selectivity.

Physisorption-based separation processes represents a promising alternative to the conventional thermally driven methods, such as cryogenic separation. However, a significant challenge lies in balancing the trade-off between adsorption capacity and selectivity of adsorbents. In this study, we introduce a novel fluorinated-anion pillared metal-organic frameworks (APMOFs) featuring a dual-pore architecture, constructed using a pyridine-oxazole bifunctional ligand. The inherent low symmetry of the ligand leads to significant distortion of the fluorinated-anion pillars, resulting in a distinctive type of APMOFs characterized by dual-pore architecture. On pore structure with constrict pore width is enriched with a high density of anion fluorinated pillars, offering numerous active sites advantageous for enhancing separation selectivity. Concurrently, the other pore structure exhibits larger dimensions, facilitating increased gas molecule accommodation and thereby augmenting adsorption capacity. Gas sorption studies reveal a substantial C2H2 adsorption capacity and a high C2H2/CO2 separation selectivity. Breakthrough experiments confirm its exceptional separation performance, while theoretical investigations elucidate a sequential adsorption process within these APMOFs, underscoring the efficacy of this strategy in overcoming trade-off limits in adsorbents.

Design and synthesis of pillared metal-organic frameworks featuring olefinic fragments.

While metal-organic frameworks (MOFs) are known primarily for their well-defined crystalline porous structures that make them desirable for a myriad of applications, they also distinguish themselves with their chemical tunability. One strategy for chemical tailoring of MOF structures is post-synthetic modification (PSM) targeting moieties present in their organic building blocks (linkers). In this context, alkene (olefinic) fragments are underrepresented in the realm of MOFs despite their extremely well-established and versatile chemistry. With the majority of reported olefinic MOFs falling into the microporous regime, the PSM opportunities involving bulkier reagents are severely limited. Herein, we report a family of UofT (University of Toronto) pillared MOFs constructed around olefinic 1,4-bis(2-(pyridin-4-yl)vinyl)benzene (BPVB) and tetrakis(4-carboxyphenyl)porphyrin (TCPP) linkers. By utilizing a variety of M(II) [M = Zn, Ni, Co] precursors, three structurally distinct frameworks were synthesized and characterized. Most notably, the nickel-based framework represents the first reported example of a stable mesoporous olefinic pillared MOF. In addition to the de novo formation of a stable pillared MOF, Ni(II) is also used in a cation exchange process to structurally reinforce zinc-based frameworks.

Pore-Environment Engineering of Pillared Metal–Organic Frameworks for Boosting the Removal of Acetylene from Ethylene

Pore-Environment Engineering of Pillared Metal–Organic Frameworks for Boosting the Removal of Acetylene from Ethylene

Solid State Machinery of Multiple Dynamic Elements in a Metal-Organic Framework.

Engineering coordinated rotational motion in porous architectures enables the fabrication of molecular machines in solids. A flexible two-fold interpenetrated pillared Metal-Organic Framework precisely organizes fast mobile elements such as bicyclopentane (BCP) (107 Hz regime at 85 K), two distinct pyridyl rotors and E-azo group involved in pedal-like motion. Reciprocal sliding of the two sub-networks, switched by chemical stimuli, modulated the sizes of the channels and finally the overall dynamical machinery. Actually, iodine-vapor adsorption drives a dramatic structural rearrangement, displacing the two distinct subnets in a concerted piston-like motion. Unconventionally, BCP mobility increases, exploring ultra-fast dynamics (107 Hz) at temperatures as low as 44 K, while the pyridyl rotors diverge into a faster and slower dynamical regime by symmetry lowering. Indeed, one pillar ring gained greater rotary freedom as carried by the azo-group in a crank-like motion. A peculiar behavior was stimulated by pressurized CO2, which regulates BCP dynamics upon incremental site occupation. The rotary dynamics is intrinsically coupled to the framework flexibility as demonstrated by complementary experimental evidence (multinuclear solid-state NMR down to very low temperatures, synchrotron radiation XRD, gas sorption) and computational modelling, which helps elucidate the highly sophisticated rotor-structure interplay.

Fabrication of Pillar‐Cage Fluorinated Anion Pillared Metal–Organic Frameworks via a Pillar Embedding Strategy and Efficient Separation of SO2 through Multi‐Site Trapping

AbstractFlue gas desulfurization is crucial for both human health and ecological environments. However, developing efficient SO2 adsorbents that can break the trade‐off between adsorption capacity and selectivity is still challenging. In this work, a new type of fluorinated anion‐pillared metal–organic frameworks (APMOFs) with a pillar‐cage structure is fabricated through pillar‐embedding into a highly porous and robust framework. This type of APMOFs comprises smaller tetrahedral cages and larger icosahedral cages interconnected by embedded [NbOF5]2− and [TaOF5]2− anions acting as pillars. The APMOFs exhibits high porosity and density of fluorinated anions, ensuring exceptional SO2 adsorption capacity and ultrahigh selectivity for SO2/CO2 and SO2/N2 gas mixtures. Furthermore, these two structures demonstrate excellent stability towards water, acid/alkali, and SO2 adsorption. Cycle dynamic breakthrough experiments confirm the excellent separation performance of SO2/CO2 gas mixtures and their cyclic stability. SO2‐loaded single‐crystal X‐ray diffraction, Grand canonical Monte Carlo (GCMC) simulations combined with density functional theory (DFT) calculations reveal the preferred adsorption domains for SO2 molecules. The multiple‐site host–guest and guest‐guest interactions facilitate selective recognition and dense packing of SO2 in this hybrid porous material. This work will be instructive for designing porous materials for flue gas desulfurization and other gas‐purification processes.

Fabrication of Pillar-Cage Fluorinated Anion Pillared Metal-Organic Frameworks via a Pillar Embedding Strategy and Efficient Separation of SO2 through Multi-Site Trapping.

Flue gas desulfurization is crucial for both human health and ecological environments. However, developing efficient SO2 adsorbents that can break the trade-off between adsorption capacity and selectivity is still challenging. In this work, a new type of fluorinated anion-pillared metal-organic frameworks (APMOFs) with a pillar-cage structure is fabricated through pillar-embedding into a highly porous and robust framework. This type of APMOFs comprises smaller tetrahedral cages and larger icosahedral cages interconnected by embedded [NbOF5]2- and [TaOF5]2- anions acting as pillars. The APMOFs exhibits high porosity and density of fluorinated anions, ensuring exceptional SO2 adsorption capacity and ultrahigh selectivity for SO2/CO2 and SO2/N2 gas mixtures. Furthermore, these two structures demonstrate excellent stability towards water, acid/alkali, and SO2 adsorption. Cycle dynamic breakthrough experiments confirm the excellent separation performance of SO2/CO2 gas mixtures and their cyclic stability. SO2-loaded single-crystal X-ray diffraction, Grand canonical Monte Carlo (GCMC) simulations combined with density functional theory (DFT) calculations reveal the preferred adsorption domains for SO2 molecules. The multiple-site host-guest and guest-guest interactions facilitate selective recognition and dense packing of SO2 in this hybrid porous material. This work will be instructive for designing porous materials for flue gas desulfurization and other gas-purification processes.

A water vapor sensor with 3D pillared metal–organic framework and 2D breathing mode

Two 3D pillared metal–organic frameworks (MOFs) [Cd2(adc)2(bpp)3·4H2O]n (1) and [Cd2(adc)2(bpp)3]n (1b) with a 2D breathing mode of reversible dehydration–rehydration have been designed and synthesized. The dynamic behavior between 1 and 1b was detected by in situ single-crystal XRD analysis, which demonstrated that this 3D pillared MOF contracted and expanded in two dimensions accompanied by dehydration–rehydration. Additionally, 1b exhibited faster water vapor response compared to commercial silica gel desiccant at room temperature (21 °C) and humidity (RH% 50), which was detected by in situ IR spectrum. Therefore, the results suggests that this kind of flexible 3D pillared metal–organic frameworks of 1 and 1b would be a reliable sensor for monitoring water vapor. (H2adc = 4,4′-azodibenzoic acid, bpp = 1,3-Di(4-pyridyl)propane).

Reversed CO2/C2H2 separation with ultrahigh carbon dioxide adsorption capacity in Zn-based pillared metal-organic frameworks

The removal of CO2 impurities from CO2/C2H2 gas mixtures to obtain high-purity acetylene used for manufacturing of various commodity chemicals, is very important for the chemical purifying of acetylene. However, CO2 and C2H2 exhibit analogous physical properties as well as molecular sizes causing their separation to become an industrially challenging process, and developing energy-efficient CO2-selective adsorbents is a class of materials of vast value. In this work, a pillared-layer ultramicroporous metal-organic framework (MOF) constructed from zinc (Ⅱ) and triazolium planar layers with oxalic acid, which has been termed as CALF-20, can preferentially absorb CO2 from C2H2. Unique pore environment and electrostatic effects enable this material foremost capture CO2. CALF-20 shows higher affinities towards CO2 than C2H2 based on heats of adsorption computed from single-component adsorption isotherms. Grand Canonical Monte Carlo simulations confirm the affinity interactions and multiple host-guest interactions between CO2 and CALF-20. Sorption experiments revealed that CALF-20 has excellent trapping volume with extremely high CO2 uptake capacity (140.2 cm3 cm−3).

Topological Design of Unprecedented Metal-Organic Frameworks Featuring Multiple Anion Functionalities and Hierarchical Porosity for Benchmark Acetylene Separation.

Separation of acetylene (C2 H2 ) from carbon dioxide (CO2 ) or ethylene (C2 H4 ) is industrially important but still challenging so far. Herein, we developed two novel robust metal organic frameworks AlFSIX-Cu-TPBDA (ZNU-8) with znv topology and SIFSIX-Cu-TPBDA (ZNU-9) with wly topology for efficient capture of C2 H2 from CO2 and C2 H4 . Both ZNU-8 and ZNU-9 feature multiple anion functionalities and hierarchical porosity. Notably, ZNU-9 with more anionic binding sites and three distinct cages displays both an extremely large C2 H2 capacity (7.94 mmol/g) and a high C2 H2 /CO2 (10.3) or C2 H2 /C2 H4 (11.6) selectivity. The calculated capacity of C2 H2 per anion (4.94 mol/mol at 1 bar) is the highest among all the anion pillared metal organic frameworks. Theoretical calculation indicated that the strong cooperative hydrogen bonds exist between acetylene and the pillared SiF6 2- anions in the confined cavity, which is further confirmed by in situ IR spectra. The practical separation performance was explicitly demonstrated by dynamic breakthrough experiments with equimolar C2 H2 /CO2 mixtures and 1/99 C2 H2 /C2 H4 mixtures under various conditions with excellent recyclability and benchmark productivity of pure C2 H2 (5.13 mmol/g) or C2 H4 (48.57 mmol/g).

Topological Design of Unprecedented Metal‐Organic Frameworks Featuring Multiple Anion Functionalities and Hierarchical Porosity for Benchmark Acetylene Separation

AbstractSeparation of acetylene (C2H2) from carbon dioxide (CO2) or ethylene (C2H4) is industrially important but still challenging so far. Herein, we developed two novel robust metal organic frameworks AlFSIX‐Cu‐TPBDA (ZNU‐8) with znv topology and SIFSIX‐Cu‐TPBDA (ZNU‐9) with wly topology for efficient capture of C2H2 from CO2 and C2H4. Both ZNU‐8 and ZNU‐9 feature multiple anion functionalities and hierarchical porosity. Notably, ZNU‐9 with more anionic binding sites and three distinct cages displays both an extremely large C2H2 capacity (7.94 mmol/g) and a high C2H2/CO2 (10.3) or C2H2/C2H4 (11.6) selectivity. The calculated capacity of C2H2 per anion (4.94 mol/mol at 1 bar) is the highest among all the anion pillared metal organic frameworks. Theoretical calculation indicated that the strong cooperative hydrogen bonds exist between acetylene and the pillared SiF62− anions in the confined cavity, which is further confirmed by in situ IR spectra. The practical separation performance was explicitly demonstrated by dynamic breakthrough experiments with equimolar C2H2/CO2 mixtures and 1/99 C2H2/C2H4 mixtures under various conditions with excellent recyclability and benchmark productivity of pure C2H2 (5.13 mmol/g) or C2H4 (48.57 mmol/g).

Synthesis of Ketjenblack Decorated Pillared Ni(Fe) Metal-Organic Frameworks as Precursor Electrocatalysts for Enhancing the Oxygen Evolution Reaction.

Metal-organic frameworks (MOFs) have been investigated with regard to the oxygen evolution reaction (OER) due to their structure diversity, high specific surface area, adjustable pore size, and abundant active sites. However, the poor conductivity of most MOFs restricts this application. Herein, through a facile one-step solvothermal method, the Ni-based pillared metal-organic framework [Ni2(BDC)2DABCO] (BDC = 1,4-benzenedicarboxylate, DABCO = 1,4-diazabicyclo[2.2.2]octane), its bimetallic nickel-iron form [Ni(Fe)(BDC)2DABCO], and their modified Ketjenblack (mKB) composites were synthesized and tested toward OER in an alkaline medium (KOH 1 mol L-1). A synergistic effect of the bimetallic nickel-iron MOF and the conductive mKB additive enhanced the catalytic activity of the MOF/mKB composites. All MOF/mKB composite samples (7, 14, 22, and 34 wt.% mKB) indicated much higher OER performances than the MOFs and mKB alone. The Ni-MOF/mKB14 composite (14 wt.% of mKB) demonstrated an overpotential of 294 mV at a current density of 10 mA cm-2 and a Tafel slope of 32 mV dec-1, which is comparable with commercial RuO2, commonly used as a benchmark material for OER. The catalytic performance of Ni(Fe)MOF/mKB14 (0.57 wt.% Fe) was further improved to an overpotential of 279 mV at a current density of 10 mA cm-2. The low Tafel slope of 25 mV dec-1 as well as a low reaction resistance due to the electrochemical impedance spectroscopy (EIS) measurement confirmed the excellent OER performance of the Ni(Fe)MOF/mKB14 composite. For practical applications, the Ni(Fe)MOF/mKB14 electrocatalyst was impregnated into commercial nickel foam (NF), where overpotentials of 247 and 291 mV at current densities of 10 and 50 mA cm-2, respectively, were realized. The activity was maintained for 30 h at the applied current density of 50 mA cm-2. More importantly, this work adds to the fundamental understanding of the in situ transformation of Ni(Fe)DMOF into OER-active α/β-Ni(OH)2, β/γ-NiOOH, and FeOOH with residual porosity inherited from the MOF structure, as seen by powder X-ray diffractometry and N2 sorption analysis. Benefitting from the porosity structure of the MOF precursor, the nickel-iron catalysts outperformed the solely Ni-based catalysts due to their synergistic effects and exhibited superior catalytic activity and long-term stability in OER. In addition, by introducing mKB as a conductive carbon additive in the MOF structure, a homogeneous conductive network was constructed to improve the electronic conductivity of the MOF/mKB composites. The electrocatalytic system consisting of earth-abundant Ni and Fe metals only is attractive for the development of efficient, practical, and economical energy conversion materials for efficient OER activity.

A new TIFSIX anion pillared metal organic framework with abundant electronegative sites for efficient C2H2/CO2separation

A new TIFSIX anion pillared metal organic framework ZNU-7 (ZNU = Zhejiang Normal University) with abundant electronegative sites was prepared for efficient C2H2/CO2separation.

Highly selective gas separation by two isostructural boron cluster pillared MOFs

• Remarkable C 2 H 2 /C 2 H 4 selectivity and high C 2 H 2 capacity in BSF-9 with reasonable illustration of the C 2 H 2 and C 2 H 4 adsorption difference by modeling study. • Excellent dynamic separation performance of C 2 H 2 /C 2 H 4 in BSF-9 with good recyclability. • High CO 2 /N 2 selectivity achieved both by BSF-4 and BSF-9 through near-sieving effect. • Inverse ambient adsorption capacity of C 3 H 8 and C 2 H 6 observed in BSF-9. • Distinct C 3 H 8 adsorption kinetics observed for BSF-4 and BSF-9. Two isostructural closo -dodecaborate [B 12 H 12 ] 2- pillared metal organic frameworks (MOFs), BSF-4 and BSF-9, were synthesized and compared in the performance of selective gas adsorption and separation. BSF-9 with symmetrical interpenetration and two contracted 1D channel exhibited efficient uptake of C 2 H 2 (85.1/76.3 mLg −1 , 278/298 K) with high separation selectivity over C 2 H 4 (41.4, 298 K), outperforming BSF-4 (7.3, 298 K) and many benchmark MOFs. The selectivity of C 2 H 6 /CH 4 , CO 2 /CH 4 , CO 2 /N 2 on BSF-9 (25.2, 9.9, 56.6) and BSF-4 (19.0, 8.9, 41.7) was all relatively high and comparable. The practical gas separation ability for C 2 H 2 /C 2 H 4 mixtures on BSF-9 was confirmed by mixed gas breakthrough experiments with negligible capacity loss after 4 cycles, indicating its potential for purification of ethylene from acetylene-containing industrial gas mixtures. The C 2 H 2 and C 2 H 4 bonding sites and bonding energies within the framework of BSF-9 were further compared by density functional theory (DFT) study, indicating that C 2 H 2 can be trapped tightly between two anionic [B 12 H 12 ] 2- by four synergistic dihydrogen bonds while C 2 H 4 only interacts with single [B 12 H 12 ] 2- with weaker bonding energy. BSF-4 with asymmetrical interpenetration and single extended 1D channel showed higher selectivity of C 3 H 8 /CH 4 (138.5, 298 K) than that of BSF-9 (64.0, 298 K). Inverse ambient adsorption capacity of C 3 H 8 < C 2 H 6 was observed in BSF-9 due to the small pore window and 1D channel.

A new boron cluster anion pillared metal organic framework with ligand inclusion and its selective acetylene capture properties

A novel microporous boron cluster pillared metal–organic framework BSF-10 was synthesized with ligand inclusion for efficient C2H2/CO2and C2H2/C2H4adsorption separation.

A robust metal-organic framework with guest molecules induced splint-like pore confinement to construct propane-trap for propylene purification

A propane-trapping pillar-layered metal–organic framework with splint-like pore confinement for propylene purification exhibits excellent separation performances of C 3 H 8 /C 3 H 6 mixture. • C 3 H 8 /C 3 H 6 -induced splint-like pore confinement can be constructed in a robust MOF. • It shows excellent separation performance of C 3 H 8 /C 3 H 6 with the record selectivity. • Breakthrough experiments indicate the complete separation of C 3 H 8 /C 3 H 6 mixture. • C 3 H 6 productivity is the highest with good regenerability in dynamic separation. • Theoretical calculations and control experiments confirm the separation mechanism. It is an extremely challenging task to capture C 3 H 8 from the C 3 H 8 /C 3 H 6 mixture, which requires an adsorbent with a specific pore structure. Herein, an ultramicroporous pillared metal–organic framework Ni(ADC)(TED) 0.5 is reported for efficient C 3 H 8 /C 3 H 6 separation. Theoretical calculations revealed that the ADC ligand may form a splint-like pore confinement structure induced by the introduction of guest molecules to construct a propane-trap in the framework. As a result, excellent separation performance for C 3 H 8 /C 3 H 6 is obtained. A record-high IAST-predicted selectivity (6.4), C 3 H 8 /C 3 H 6 uptake ratio (111.0%), C 3 H 8 Henry constant (2159.2 mmol g −1 bar −1 ), and separation potential (1943.0 mmol L -1 ) exceed those in porous adsorbents reported so far. Breakthrough experiments indicate that Ni(ADC)(TED) 0.5 can completely separate C 3 H 8 /C 3 H 6 mixture with the highest C 3 H 6 productivity (0.085 mmol g −1 ) and good regenerability. These results show that this material has great potential application in C 3 H 8 /C 3 H 6 separation.

Insights into Paraben Adsorption by Metal-Organic Frameworks for Analytical Applications.

Metal-organic frameworks (MOFs) are attractive materials used as sorbents in analytical microextraction applications for contaminants of emerging concern (CECs) from environmental liquid matrices. The demanding specs for a sorbent in the analytical application can be comprehensively studied by considering the interactions of the target analytes with the frameworks by the use of single-crystal X-ray diffraction, computational analysis, and adsorption studies, including the kinetic ones. The current study intends a better understanding of the interactions of target CECs (particularly, propylparaben (PPB) as a model) and three Zn-based layered pillared MOFs: CIM-81 [Zn2(tz)2(bdc)] (Htz = 1,2,4-triazole and H2bdc = 1,4-benzenedicarboxylic acid) and their amino derivatives [Zn2(NH2-tz)2(bdc)] CIM-82 and [Zn2(tz)2(NH2-bdc)] CIM-83 (NH2-Htz = 3-amino-1,2,4-triazole and NH2-H2bdc = 2-amino-1,4-benzenedicarboxylic acid). The crystal structures of the two solvate compounds (dma@CIM-81 (dma = dimethylacetamide) and acetone@CIM-81) were solved by single-crystal X-ray diffraction to determine the points of interaction between the framework and the guest molecules. They also served as a starting point for the computational modeling of the PPB@CIM-81 compound, showing that up to two PPB molecules can be hosted in one of the pores, while only one can be trapped in the second pore type, leading to a maximum theoretical capacity of 291.9 mg g-1. This value is close to the value obtained by the adsorption isotherm experiment for CIM-81 (283 mg g-1). This value is, by far, higher than those previously reported for other materials for the removal of PPB from water, and also higher than the experimental values obtained for CIM-82 (54 mg g-1) and CIM-83 (153 mg g-1). The kinetics of adsorption is not very fast, with uptake of about 40% in 3 h, although a 70% release in methanol is achieved in 1 h. In addition, a further comparison of performance in analytical microextraction (requiring only 10 mg of CIM-81) was carried out together with chromatographic analysis to support all insights attained, with the method being able to monitor CECs as low as μg L-1 levels in complex environmental water samples, thus performing successfully for water monitoring even in multicomponent scenarios.

A pillared metal-organic framework with rich π-electron linkers as a novel fluorescence probe for the highly selective and sensitive detection of nitroaromatics

Fast and selective recognition of nitro explosives (NEs) is an emerging issue of interest. Among different detection systems, pillared metal-organic frameworks (MOFs) demonstrated high applicability in the detection of NEs. A novel pillar-layered MOF, specifically {[Zn2(2,6-NDC)2(dabco)].7DMF·3H2O} (TMU-14) were synthesized by solvothermal reaction of Zn(II) nitrate hexahydrate, 2,6-naphthalenedicarboxylic acid (2,6-NDC) as the O-donor ligand and 1,4-diazabicyclo[2.2.2]octane (dabco) as the N-donor ligand. This MOF was characterized through Single Crystal X-ray crystallography. This study demonstrated that TMU-14 with a 3D layered structure and a suitable pore window of 10.933 A˚ was an efficient luminescent sensory material through host-guest complexation with good stability and recyclability for the detection of NEs with high quantum yield.

Effective Separation of Prime Olefins from Gas Stream Using Anion Pillared Metal Organic Frameworks: Ideal Adsorbed Solution Theory Studies, Cyclic Application and Stability

The separation of C3H4/C3H6 is one of the most energy intensive and challenging operations, requiring up to 100 theoretical stages, in traditional cryogenic distillation. In this investigation, the potential application of two MOFs (SIFSIX-3-Ni and NbOFFIVE-1-Ni) was tested by studying the adsorption-desorption behaviors at a range of operational temperatures (300–360 K) and pressures (1–100 kPa). Dynamic adsorption breakthrough tests were conducted and the stability and regeneration ability of the MOFs were established after eight consecutive cycles. In order to establish the engineering key parameters, the experimental data were fitted to four isotherm models (Langmuir, Freundlich, Sips and Toth) in addition to the estimation of the thermodynamic properties such as the isosteric heats of adsorption. The selectivity of the separation was tested by applying ideal adsorbed solution theory (IAST). The results revealed that SIFSIX-3-Ni is an effective adsorbent for the separation of 10/90 v/v C3H4/C3H6 under the range of experimental conditions used in this study. The maximum adsorption reported for the same combination was 3.2 mmol g−1. Breakthrough curves confirmed the suitability of this material for the separation with a 10-min gab before the lighter C3H4 is eluted from the column. The separated C3H6 was obtained with a 99.98% purity.

Efficient adsorption separation of methane from CO2 and C2–C3 hydrocarbons in a microporous closo-dodecaborate [B12H12]2- pillared metal–organic framework

A closo-dodecaborate [B12H12]2- functionalized metal organic framework (MOF), BSF-3, constructed by the self-assembly of the Cu(II) cation, 1,4-di(pyridin-4-yl)benzene linker and cluster [B12H12]2- pillar was investigated for the adsorption separation of light hydrocarbons. The activated MOF exhibited efficient uptake of CO2 and C2–C3 hydrocarbons with high separation selectivity of C3H8 (138), C2H2 (205), C2H4 (23), C2H6 (13) and CO2 (9) over CH4, outperforming many popular MOFs. The practical gas separation ability for C2H2/CH4, CO2/CH4 and C3H8/C2H6/CH4 was confirmed by mixed gas breakthrough experiments with no capacity loss after 7 cycles, indicating its potential for purification of methane from natural gas and pyrolysis gas. The gas bonding sites within the framework were further studied by modelling studies, which indicated that the anionic [B12H12]2- pillar contributed the most to capturing hydrocarbon molecules by multiple B-Hδ-···Hδ+-C interactions.

High Purity/Recovery Separation of Propylene from Propyne Using Anion Pillared Metal-Organic Framework: Application of Vacuum Swing Adsorption (VSA)

Propylene is one of the world’s most important basic olefin raw material used in the production of a vast array of polymers and other chemicals. The need for high purity grade of propylene is essential and traditionally achieved by the very energy-intensive cryogenic separation. In this study, a pillared inorganic anion SIF62− was used as a highly selective C3H4 due to the square grid pyrazine-based structure. Single gas adsorption revealed a very high C3H4 uptake value (3.32, 3.12, 2.97 and 2.43 mmol·g−1 at 300, 320, 340 and 360 K, respectively). The values for propylene for the same temperatures were 2.73, 2.64, 2.31 and 1.84 mmol·g−1, respectively. Experimental results were obtained for the two gases fitted using Langmuir and Toth models. The former had a varied degree of representation of the system with a better presentation of the adsorption of the propylene compared to the propyne system. The Toth model regression offered a better fit of the experimental data over the entire range of pressures. The representation and fitting of the models are important to estimate the energy in the form of the isosteric heats of adsorption (Qst), which were found to be 45 and 30 kJ·Kmol−1 for propyne and propylene, respectively. A Higher Qst value reveals strong interactions between the solid and the gas. The dynamic breakthrough for binary mixtures of C3H4/C3H6 (30:70 v/v)) were established. Heavier propylene molecules were eluted first from the column compared to the lighter propyne. Vacuum swing adsorption was best suited for the application of strongly bound materials in adsorbents. A six-step cycle was used for the recovery of high purity C3H4 and C3H6. The VSA system was tested with respect to changing blowdown time and purge time as well as energy requirements. It was found that the increase in purge time had an appositive effect on C3H6 recovery but reduced productivity and recovery. Accordingly, under the experimental conditions used in this study for VSA, the purge time of 600 s was considered a suitable trade-off time for purging. Recovery up to 99%, purity of 98.5% were achieved at a purge time of 600 s. Maximum achieved purity and recovery were 97.4% and 98.5% at 100 s blowdown time. Energy and power consumption varied between 63–70 kWh/ton at the range of purge and blowdown time used. The VSA offers a trade-off and cost-effective technology for the recovery and separation of olefins and paraffin at low pressure and high purity.